During this fiscal year a few modifications have been made in order to improve the performance and versatility of the SEMS instrument. These modifications included: 1) Cs+ ion gun for comparative study of the secondary ion formation under bombardment by particles of different nature; 2) Faraday cup to measure the intensity of primary ion beam more precisely; 3) conversion dinode multiplier and immersion lens to improve secondary ion detection; 4) differential vacuum system for the MS/MS portion of the instrument. Experimental studies of the particle desorption ionization of labile compounds continued on the instrument, including studies of the primary beam parameters in relation to the resulting mass spectra of the target material. Some of recent biological applications included demonstrating the utility of the SEMS system for biological extract analysis in studies involving the drug induced Parkinsonism in primates and humans. A new direction in the instrument application has been undertaken this year: an application as a molecular microscope - a device which will detect the spatial distribution of organic substances on the surfaces of biological specimens. The instrument design was presented at the Annual Conference on Mass Spectrometry and Allied Topics on June 1, 1984 in San Antonio, Texas.